Currently, Li-ion batteries have been used in green vehicles, such as electric vehicles (EVs) and hybrid electric vehicles (HEVs). The workable voltage of a single cell in a Li-ion battery is approximately 3-4 volts, but EVs and HEVs usually require higher voltages up to more than 100 volts. Usually, multiple cells are coupled to each other in series to drive EVs and HEVs.
For battery management, a number of cells are arranged as one or more battery packs, and an analog front end (AFE) device is coupled to each battery pack to assess the status of the battery packs or the cells, such as their voltage and temperature. Digital data indicating the status of the battery packs or the cells is transferred to a microprocessor for various purposes such as battery protection. A communication bus between the microprocessor and each AFE device is also needed.
FIG. 1 shows a conventional battery management system 100 with an opto-coupler based vertical bus. The AFE devices 122, 124 and 126 are coupled to the battery packs 112, 114, and 116, respectively, for accessing the status of each cell in the battery packs. Opto-coupler blocks 132, 134, and 136 establish a communication bus between the AFE devices 122, 124, and 126 and a central electronics control unit (CECU) 140. Each opto-coupler block includes two opto-couplers for each wire of the bus.
The conventional battery management system 100 with an opto-coupler based vertical bus suffers from high cost and high power consumption since opto-couplers are relatively expensive and their driving capability requires mille-amperes of current.